Which algorithm can be used for extracting text patterns in tabular data?
You should first segregate the rejected samples. You can use then use string matching or something more complex (like creating embeddings and then, taking L2 distance between them) between the different field names you have and the comment for rejection. Whichever field gets the highest score, you increase the rejection count for that field. In the end, you will have a tally of who is your biggest enemy.
You can create some rules which prevent injection of wrong data (like your password should be 7 characters long or something along these lines) or post-process your entries to match a uniform format.